In cellular networks, e.g., as specified by 3GPP (3rd Generation Partnership Project), multicast and broadcast transmission modes have been introduced, e.g., for the purpose of delivering multimedia content. An example of such broadcast and multicast transmission mode is the Multimedia Broadcast Multicast Service (MBMS), e.g., as specified in 3GPP TS 22.346 V11.0.0 (2012-09) and 3GPP TS 23.246 V12.0.0 (2013-12).
In the MBMS architecture as defined in 3GPP TS 23.346, a gateway node, referred to as MBMS-GW, which distributes MBMS data to radio access network (RAN) nodes, also interacts with a control node referred to as MME (Mobility Management Entity). For this purpose, an interface referred to as Sm is provided between the MBMS-GW and the MME. The Sm interface is based GTP (GPRS Tunneling Protocol) and UDP (User Datagram Protocol), which makes the Sm interface susceptible to network disturbance. If the connection between the MBMS-GW and the MME via the Sm interface fails, this for example has the effect that the MBMS-GW is not able to send messages to the MME, and therefore it is for example not possible to start, stop, or modify MBMS sessions which are controlled by this MME.
In 3GPP TS 23.007 V12.4.0 (2014-03) procedures for handling a failure of the Sm interface is specified. These procedures involve using a maximum path failure duration timer in the MME, which is started when the MME detects the failure of the Sm interface, and a maximum path failure duration timer in the MBMS-GW, which is started when the MBMS-GW detects the failure of the Sm interface. During a transient failure of the Sm interface (in which the connection between the MBMS-GW and the MME recovers before the maximum path failure duration timer in the MBMS-GW expires), the MBMS-GW may select an alternative MME and send new MBMS Session Start Request to this alternative MME. In the case of a MBMS Session Update Request or MBMS Session Stop Request, the MBMS-GW may select an alternative MME, send a MBMS Session Start Request message to this alternative MME and, if successful, send subsequently the MBMS Session Update Request or MBMS Session Stop Request to this alternative MME. After having selected an alternative MME, the MBMS-GW shall consider the MME answering to the MBMS Start Request as the controlling MME for the MBMS session and send any subsequent MBMS Session Update or MBMS Session Stop for this MBMS Session to this MME. When detecting a non-transient Sm path failure (in which the connection between the MBMS-GW and the MME does not recover before the maximum path failure duration timer in the MBMS-GW expires), the MBMS-GW may move the control of all the affected active MBMS sessions to an alternative MME. The alternative MME is selected from the same MME pool as the original MME to which the connection over the Sm interface failed.
According to 3GPP TS 23.007, the maximum path failure duration timer of the MBMS-GW should be configured with a shorter value than the maximum path failure duration timer of the MME to avoid interrupting active MBMS sessions upon a non-transient Sm path failure. This also means that any reaction to the non-transitory failure will first occur at the MBMS-GW.
In the above way of handling the non-transitory failure of the Sm interface, MBMS-GW re-establishes not only the control plane with the alternative MME, but also re-establishes the user plane, even if the user plane may actually be unaffected by the network disturbance which resulted in failure of the Sm interface. This may adversely affect user experience. Further, if no alternative MME is available, all user plane traffic of the MBMS session will be stopped. Further, the re-establishment of the control plane may result in a situation in which that parts of the control plane with the old MME co-exist with the newly established control plane. Such parts may for example be control plane sessions between the old MME and radio access network (RAN) nodes, such as MCEs (Multicast Coordination Entities). This ambiguity may cause various problems. For example, an interface failure between an MCE and the old MME may trigger a complete re-establishment of the control plane with the old MME. Further, an interface failure between an MCE and both the old MME and new MME may have the effect that the MCE does not know which one is the current controlling MME and incorrect selection of the old MME when re-establishing the control plane from the MCE. Such issues may be addressed by causing the MCE to reset the old MME once the new MME assumes control responsibility. However, since the number of MCEs involved in an MBMS session may be huge, this may cause undesirable signaling overhead.
Accordingly, there is a need for techniques which allow for efficiently addressing an interface failure between a gateway and control node which are handling multicast transmissions in a cellular network.